(a) Technical Field
The present invention relates to a fuel cell stack and, more particularly, to a fuel cell stack in which machining accuracy of a cooling medium guide channel is enhanced in a guide region of each separator, and a cooling medium is effectively distributed to significantly enhance heat transmission efficiency.
(b) Description of the Related Art
A fuel cell includes a fuel cell stack producing electrical energy, a fuel supply system supplying fuel (hydrogen) to the fuel cell stack, an air supply system including an air blower and a humidifier to supply oxygen in the air, an oxidizer required for an electrochemical reaction to the fuel cell stack, and a heat and water management system controlling an operation temperature of the fuel cell stack.
As illustrated in FIG. 1 (RELATED ART), the fuel cell stack is formed by stacking a plurality of unit fuel cells 40, and the unit fuel cells 40 each have a membrane electrode assembly (MEA) 10 and a pair of separators 20 and 30 tightly attached to opposing surfaces of the MEA 10.
The MEA 10 includes a solid polymer electrolyte membrane enabling a hydrogen proton to move and catalytic layers, that is, a cathode and an anode, applied to opposing surfaces of the electrolyte membrane such that hydrogen and oxygen may react with each other.
A gas diffusion layer (GDL) is positioned on outer surfaces of the MEA 10, that is, portions where the cathode and the anode are positioned, and the pair of separators 20 and 30 is positioned on outer sides of the GDL.
The pair of separators 20 and 30 has reacting gas channels 23 and 33 supplying a reacting gas (fuel or air) and discharging water produced according to a reaction, respectively.
The pair of separators 20 and 30 include a cathode separator 20 tightly attached to the cathode of the MEA 10 and an anode separator 30 tightly attached to the anode of the MEA 10.
A cathode reacting surface is formed on one surface of the cathode separator 20 and a plurality of air channels 23 supplying air as an oxidizer to the cathode of the MEA 10 are formed on the cathode reacting surface. A cathode cooling surface is formed on the other surface of the cathode separator 20, and a plurality of cooling channels 24 distributing a cooling medium are formed on the cathode cooling surface.
An anode reacting surface is formed on one surface of the anode separator 30, and a plurality of fuel channels 33 supplying fuel to the anode of the MEA 10 are formed on the anode reacting surface. An anode cooling surface is formed on the other surface of the anode separator, and a plurality of cooling channels 34 distributing a cooling medium are formed on the anode cooling surface.
In the fuel cell stack, as the plurality of unit fuel cells 40 are stacked in a vertical direction, the cathode separator 20 of one unit fuel cell 40 and the anode separator 30 of the other unit fuel cell 40 are adhered to face each other between adjacent MEAs 10, and in particular, the cooling channels 24 of the cathode separator 20 and the cooling channels 34 of the anode separator 30 join to form cooling passages 24 and 34 for distributing a cooling medium, and accordingly, a pair of cooling passages 24 and 34 is symmetrically disposed on opposing sides of each of the MEAs 10.
FIG. 2 (RELATED ART) is a plan view illustrating a portion of a cooling surface of a conventional cathode separator.
As illustrated in FIG. 2, a plurality of manifolds 7, 8, and 9 are provided in at least one end of each of the separators 20 and 30, and the plurality of manifolds 7, 8, and 9 may be an air manifold 7, a cooling medium manifold 8, and a fuel manifold 9.
A cooling surface (or reacting surface) of each of the separators 20 and 30 includes a guide region 4 adjacent to the plurality of manifolds 7, 8, and 9 and a reacting region 2 in which an electrochemical reaction takes place. The reacting region 2 may need to secure predetermined contact pressure to move electricity produced according to the electrochemical reaction, and the guide region 4, in which an electrochemical reaction does not take place, is configured to simply guide flow of a fluid (air, fuel, or cooling medium) between the manifolds and the reacting region 2.
In order to smoothly distribute a reacting gas, the plurality of reacting gas channels 23 and 33 are formed to continue from the guide region 4 to the reacting region 2 on the reacting surfaces of the separators 20 and 30, whereby the reacting gas channels in the guide region 4 and the reacting gas channels in the reacting region 2 are respectively matched (i.e., in a one-to-one manner).
Since the plurality of manifolds 7, 8, and 9 are formed in the ends of the separators 20 and 30, the guide region 4 has an area narrower than that of the reacting region 2. Thus, as the plurality of reacting gas channels are intended to be continuously formed from the guide region 4 to the reacting region 2 on the reacting surfaces of the separators 20 and 30, the plurality of cooling channels 24 and 34 are inevitably formed to continue from the guide region 4 to the reacting region 2 on the cooling surfaces opposing the reacting surfaces. However, as illustrated in FIG. 2, pitches between the cooling channels 24 and 34 are so narrow that the cooling channels 24 and 34 are very difficult to form.
In particular, in a case where the cooling channels 24 and 34 of the separators 20 and 30 are formed through stamping by using a thin plate material with low elongation, if pitches between the cooling channels are 1.5 or less, it is very difficult to process the cooling channels and cracks may readily occur in the cooling channels.
Thus, in the related art separators 20 and 30, formability of the cooling channels 24 and 34 in the narrow guide region 4 is lowered, which leads to a reduction in the number of cooling channels 24 and 34. This, however, may degrade an effective distribution of a cooling medium or heat transmission efficiency, resulting in deterioration of overall efficiency of a fuel cell.